(sapping,sapped)to make something/somebody weaker; to destroy something graduallysap somethingThe hot sun sapped our energy.The fever slowly sapped her strength.sap somebody (of something)Years of failure have sapped him of his confidence.Word OriginverbOld Englishsæp, probably of Germanic origin. The verb (dating from the mid 18th cent.) is often interpreted as a figurative use of the notion “drain the sap from”, but is derived originally from the verb sap, in the sense ‘undermine’.